Emulsifiers used in food products include surfactants such as soybean lecithin, glycerin fatty acid esters, sucrose fatty acid esters and the like. These low molecular emulsifiers are widely used for preparation of oil-in-water emulsions which have oil stably dispersed in an aqueous phase, forming stably dispersed emulsions with the hydrophobic regions in the emulsifiers adsorbed onto the oil-phase interface and the hydrophilic regions directed toward the aqueous phase. These emulsifiers exhibit very powerful emulsifying power, allowing preparation of satisfactory emulsions with small emulsified particle sizes.
Such emulsions maintain stable emulsified states when used under non-diluted conditions such as in creams. However, in the case of food products consisting of highly diluted emulsions, such as emulsified flavorings in beverages, the emulsified state readily disintegrates and the heating stability and acid stability which are a requirement for emulsifiers are insufficient, and for these reasons they have not been used very much in practice.
Currently, gum arabic is commonly used as a natural macromolecular emulsifier for emulsified flavorings (Non-patent documents 1-2).
Gum arabic is reported to be a glycoprotein comprising a polypeptide chain composed of hydroxyproline and serine as the major constituent amino acids bonded to an arabinogalactan chain consisting of the acidic sugar glucuronic acid and its 4-O-methylated form as constituent sugars (Non-patent document 3).
The sugar chains of gum arabic function as hydrophilic groups while the polypeptides bonded to the sugar chains function as hydrophobic groups, thereby stabilizing O/W emulsions (Non-patent document 4).
The sugar chains of emulsions prepared using gum arabic form thick hydrophilic layers at oil droplet interfaces, and since there is little separation of the gum arabic at the oil droplet interfaces even with high degrees of dilution, it is an excellent emulsifier for emulsified flavorings. However, because the Acacia sap gum arabic is only produced in certain regions and is susceptible to weather conditions, it has not been possible to sustain stable volumes and prices.
On the other hand, soybean-derived water-soluble polysaccharides function as natural macromolecular emulsifiers (Patent document 1), and are used in the field of food products as a substitute for the emulsifier function of gum arabic. However, the “emulsifying power” for obtaining emulsions with small particle sizes is currently insufficient compared to synthetic low molecular emulsifiers and the like, and therefore a need exists for natural macromolecular emulsifiers that exhibit not only high emulsifying stability but also strong emulsifying power. Conjugation of proteins and sugars by aminocarbonyl reaction has been proposed as a method of improving functions such as emulsification (Patent document 2), but this is still impractical in terms of both production and function.    Patent document 1: Japanese Unexamined Patent Publication No. 6-121922    Patent document 2: Japanese Unexamined Patent Publication No. 9-107886    Non-patent document 1: Ray et al., Food Hydrocolloids, 9(2), 123-131, 1995    Non-patent document 2: Trubiano, Flavor Technology: ACS Symposium Series 610. Washington D.C.: American Chemical Society. P198-209, 1995    Non-patent document 3: Williams, P. A. et al., Gum arabic. In Handbook of hydrocolloids    Non-patent document 4: Glicksman, Food Hydrocolloids. Boca Raton, Fla.: CRC Press. P7-30, 1983